Current spacecraft often employ large, phased-array antennas to perform reconnaissance missions, collect radar images, track ground-based and air-based targets and provide high bandwidth communications. These large, phased-array antennas are made up of a large plurality of independent antenna elements. The surfaces forming the phased-array antenna must be maintained very flat or the distortion in the antenna surface must be known to within a very small fraction of the wavelength corresponding to the operational frequency of the antenna (e.g., one-thirtieth of the wavelength for space-based radar at 10 GHz=1 mm flatness tolerance) in order for the antenna to perform correctly. In particular, for space-based radar (SBR) applications, a very high degree of surface planarity must be maintained to enable the effective use of ground clutter suppression algorithms. A high degree of surface planarity is also critical for space-based optics applications and ground moving target tracking applications.
Present day large, phased-array antennas achieve this required flatness by using high stiffness structural designs (i.e., trusses) that add significant weight and volume to the antenna when it is stowed in a launch vehicle. As will be appreciated, as the antenna area increases, the stowed volume of the array limits the antenna size due to the restrictions imposed by the launch vehicle fairing within which the stowed antenna must fit.
Other systems for measuring the flatness of planar structures have relied on metrology devices that measure the distance from a common source to pre-determined points on the structure, typically through laser reflection from a surface mounted target. For large, deployable, space-based phased-array antenna systems, there is a need for a measurement system that does not interfere with the operation of the antenna, and which provides feedback, in real time, and which further does not add significantly to the complexity of the antenna system or to the spacecraft with which it is associated.
Accordingly, it is a principal object of the present invention to provide a system for compensating for deformation occurring in a large, phased-array antenna which eliminates the need for large and heavy structural members, such as trusses, to maintain the planarity of the antenna when the antenna is subjected to external factors which would otherwise cause a deformation of its surface.
It is another object of the present invention to provide an apparatus and method for electronically compensating, in real time, for the deformation experienced by a large, phased-array antenna through non-intrusive means which permit the deformation to be monitored and suitable corrections generated to provide needed phase shifting or time delay of the signals transmitted by or received by the phased-array antenna.
It is still another object of the present invention to provide a system for detecting and compensating for the deformation occurring in a large, phased-array antenna, in real time, without significantly complicating the construction of the antenna and without impeding the ability of the antenna to be deployed in space-based applications.